This invention relates to electrostatographic reproduction machines, and more particularly to such a reproduction machine having a sheet stalling preventing transfer station placement assembly for placing low stiffness and high stiffness sheets to the toner image transfer station at a common angle without sheet stalling and resulting image smearing.
In a typical electrophotographic printing process, a aphotoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member or photoreceptor. After the electrostatic latent image is recorded on the photoreceptor, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roll or to a latent image on the photoreceptor. The toner attracted to a donor roll is then is copy sheet that must be fed and placed into contact with the photoreceptor. After such transfer, the toner particles are then heated by a fusing apparatus to permanently affix them to the copy sheet.
Because the copy can be one of a variety of such copy sheets which vary in thickness, weight and hence stiffness, feeding and placing copy sheets against the photoreceptor at the transfer station ordinarily is a difficult and problematic task. This is because relatively low stiffness copy sheets ordinarily require a steep contact angle with the photoreceptor in order to insure paper flatness against the photoreceptor as well as effective toner image transfer, while for similar flatness, relatively high stiffness copy sheets require a much lower contact angle. It has been found that the pre-transfer station nip assembly drive force that would ordinarily be required to bend the high stiffness copy sheet is so high that the copy sheet will tend to stall when it is released by the pre-transfer station nip assembly, thus resulting in copy sheet jams and causing image smear.
Thus high stiffness copy sheets cannot be effectively placed against the photoreceptor at the same high contact angle as low stiffness copy sheets. It is thus relatively difficult and costly to design transfer area effective and economical copy sheet forwarding and placement assemblies that can handle copy sheets of a wide range of stiffness without adjustment.
There is therefore a need for a reproduction machine having a sheet stalling preventing transfer station placement assembly for effectively placing low stiffness and high stiffness sheets to the toner image transfer station at a common angle without sheet stalling and resulting image smearing.